Conventionally, an electrolyte such as salt or sodium carbonate and a nonelectrolyte such as sugar or alcohol are often added to and mixed with a polar solvent such as water or the like in the food industry and the pharmaceutical industry. Further, in the medical care field, a water solution in which sodium chloride as an electrolyte, glucose as a nonelectrolyte and other small amounts of components are dissolved is utilized as a dialysate used for a dialysing treatment.
When these products are manufactured, since it is difficult to directly measure the concentration of nonelectrolytes in the solutions the electrolytes and the nonelectrolytes in the solution have conventionally been set to given concentrations, respectively by adding predetermined amounts of electrolytes and nonelectrolytes to a predetermined amount of water or a polar solvent which is calculated to have a given concentrations.
However, in this method, because the electrolytes and the like absorb water and change weight while they are stored and further weighing errors are caused by the vibration of a balance and the like, even if the predetermined amounts of electrolytes and nonelectrolytes are weighed, the concentration of a resulting solution is not accurately made to a given concentration. In addition, each time a necessary amount of the solution is changed, necessary amounts of electrolytes, nonelectrolytes, water and the like must be recalculated.
Further, for example, as to the dialysate, medicines used in the preparation of the dialysis solution have conventionally been divided into a so-called agent A mainly composed of sodium chloride and a so-called agent B composed of sodium hydrogencarbonate and they have been supplied to medical sites as undiluted solutions of given concentrations in a liquid state. Therefore, in the medical sites, the dilution ratios for the thus supplied undiluted solutions of agent A and agent B were calculated based on the respective concentrations and the dialysate was prepared by stirring and mixing predetermined amounts of the respective undiluted solutions with a predetermined amount of diluting water in a preparation tank.
Recently, however, there is a proposal in which the agent A and agent B used in the preparation of the dialysate are supplied in a powder state to medical institutions, and the dialysate having a given concentration is prepared at the medical sites by dissolving these powdered medicines in water, respectively, to make a liquid agent A and a liquid agent B each having a given concentration and thereafter mixing these liquid agents A and B.
Various methods are available to measure the concentration of electrolytes such as sodium hydrogen-carbonate used as agent B, and in particular, an electric conductivity meter is widely used because it has many advantages such as a simple construction, easy handling and high reliability resulting from a lower number of factors by which a measured value is influenced.
Therefore, in the preparation of the dialysate, the concentration of a water solution containing the agent B composed of sodium hydrogencarbonate can be simply measured using the electric conductivity meter or the like. On the other hand, the agent A mainly composed of sodium chloride contains grape sugar (glucose) as a nonelectrolyte in addition to sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium acetate etc. as electrolytes. It has conventionally been thought impossible to measure the concentration of the glucose in a water solution containing the agent A using an electric conductivity meter.
That is, the electric conductivity meter is not applicable to nonelectrolytes which are not dissociated to generate ions because the electric conductivity meter uses an electric current flowing through a solution due to the ions generated by the dissociation of substances dissolved in a polar solvent such as water.
Although refractometers, polarimeters and the like are as instruments for directly measuring the concentration of nonelectrolytes in a solution, these instruments are disadvantageous in that they are complex in construction, difficult to handle, have low reliability and measured values are liable to vary depending upon how samples are prepared.
Therefore, concerning the agent A of a dialysate, as described above, predetermined amounts of sodium chloride (electrolyte) etc. and glucose (nonelectrolyte) determined by calculation are added to a predetermined amount of water calculated to have a given concentration, thereby the electrolytes and the nonelectrolyte in the water solution are set to given concentrations, respectively.
Consequently, there arises the same problems as the above in the preparation of the dialysing solution, that is, because the amount of the liquid is increased by the dissolution of the nonelectrolyte, the electrolytes such as sodium chloride etc. and glucose or the like absorb water to change their weight while being stored, as well as weighing errors caused by the vibration of the balance, even if predetermined amounts of electrolytes and glucose are weighed, the concentration of the resulting solution is not accurately set to a given concentration. Furthermore, each time a necessary amount of a solution is changed, necessary amounts of electrolytes, nonelectrolyte, water and the like must be recalculated.